Flotation machine and impeller therefor

ABSTRACT

An impeller for a flotation machine having a circular lower plate with a central hole for supplying air through a hollow shaft to the underside, and a circular upper plate having a larger central hole and sloping downwardly toward the outside, together with a series of radial, upright vanes between the plates which are thicker at their outer edges than at their inner edges, both of which are rounded, and a series of shorter, radial fingers depending from the periphery of the lower plate, also thinner at their inner rounded edges and thicker at their outer rounded edges. This impeller is utilized with a stabilizer including outwardly extending vanes which are thicker at their inner rounded edges and thinner at their outer edges. The vanes and fingers include central metal plates reinforced at their outer edges by rods, with the vane plates and vane rods being welded between the impeller plates and the finger plates and finger rods being welded to the lower side of the under plate, to form a skeleton. The impeller skeleton may be covered with rubber, which may be formed to provide the thickness and rounded edges of the vanes and fingers. Also, the stabilizer vanes may be formed of center plates welded to a support bar structure extending around either the outside of the vanes or disposed angularly of the lower outer corner thereof. The stabilizer vanes and support bars may be covered with rubber, which may be molded to provide the desired rounded inside edge and variations in thickness. Both the stabilizer vanes and the impeller are spaced above the bottom of the tank of the flotation machine, so that a recirculation of pulp around and above the impeller between the stabilizer vanes is obtained, as well as an outward discharge of pulp by the depending fingers into the spaces between the stabilizer vanes. Not only is the efficiency increased, but also the problem of &#39;&#39;&#39;&#39;sanding up&#39;&#39;&#39;&#39; in the bottom of the tank is overcome.

United States Patent [191 Green [11] 3,843,101 Oct. 22, 1974 [5 1 FLOTATION MACHINE AND IMPELLER THEREFOR [76] Inventor: Charles A. Green, Apartado 82,

Chihuahua, Mexico [22] Filed: Oct. 30, 1972 [21] Appl. No.: 301,883

[.52.]. HES-1;- .-;%52 .9- 122l2fit i2 l9lj 219/221 51 Int. Cl B0lf5/16 5s FieldofSearch 259/96, 95, 107, 10s, 6,

[56] References Cited UNITED STATES PATENTS 1,354,489 10/1920 Johnson 259/108 2,031,590 2/1936 259/24 2,243,309 5/1941 259/8 3,690,621 9/1972 Tanaka I: 259/96 Primary ExaminerRobert W. Jenkins Attorney, Agent, or Firm-Horace B. Van

Valkenburgh; Frank C. Lowe [5 7 ABSTRACT both of which are rounded, and a series of shorter, radial fingers depending from the periphery of the lower plate, also thinner at their inner rounded edges and thicker at their outer rounded edges. This impeller is utilized with a stabilizer including outwardly extending vanes which are thicker at their inner rounded edges and thinner at their outer edges. The vanes and fingers include central metal plates reinforced at their outer edges by rods, with the vane plates and vane rods being welded between the impeller plates and the finger plates and finger rods being welded to the lower side of the under plate, to form a skeleton. The impeller skeleton may be covered with rubber, which may be formed to provide the thickness and rounded edges of the vanes and fingers. Also, the stabilizer vanes may be formed of center plates welded to a support bar structure extending around either the outside of the vanes or disposed angularly of the lower outer corner thereof. The stabilizer vanes and support bars may be covered with rubber, which may be molded to provide the desired rounded inside edge and variations in thickness. Both the stabilizer vanes and the impeller are spaced above the bottom of the tank of the flotation machine, so that a recirculation of pulp around and above the impeller between the stabilizer vanes is obtained, as well as an outward discharge of pulp by the depending fingers into the spaces between the stabilizer vanes. Not only is the efficiency increased, but also the problem of sanding up in the bottom of the tank is overcome.

16 Claims, 4 Drawing Figures 11. .4.1!!!" I my I. II In ?ATENTEBBBI22 1914 3.8431101 sum 1 0F 2 This invention relates to flotation machines which are utilized in separating mineral to be recovered, from gangue or waste, through the lifting of desired particles by bubbles of air or other suitable gas, with the addition of suitable reagents which insure or assist in the frothing and lifting of the particles.

For flotation, the raw ore is ground or otherwise comminuted to a relatively small size, such as to below 1/4 inch in size to micron sizes.

Prior flotation machines have had a tendency to sand up, i.e. the ground ore tends to collect in the bottom of a flotation cell and tends to render the machine ineffective, sometimes even stalling the impeller of the machine. The coarse particles more usually produce sanding difficulties, although this problem is not unknown with fine particles. In addition to the difficulties in operation, the tendency for the machine to sand up also decreases its efficiency and effectiveness in removing the desired particles. In addition, the level of pulp in most flotation machines tends to oscillate upwardly and downwardly, thereby decreasing both the effectiveness and efficiency of the machine.

Among the objects of this invention are to provide a novel flotation machine and impeller therefor; to provide such a flotation machine in which the tendency for sanding up is materially decreased; to provide such a flotation machine in which the effectiveness and efficiency is increased; to provide such a flotation machine in which the tendency for the pulp level to oscillate is decreased; to provide a novel impeller for a flotation machine; to provide such an impeller which will, with an appropriatestabilizer or diffusion vanes, tend to alleviate the problem of sanding up; and to provide such an impeller which is effective and efficient in operation.

In accordance with this invention, the impeller of the flotation machine is provided not onlywith a lower agitating and pumping section at which the aeration gas is supplied, but also an upper pumping section which recirculates the pulp from its center outwardly and through the stabilizer or diffuser into which the lower aeration and pumping section discharges. Such recirculation of the pulp, which has previously been agitated and forced outwardly, not only increases the recovery rate and efficiency of the machine, but also decreases the tendency for the pulp level to oscillate.

A preferred embodiment of this invention is illustratedin the accompanying drawings, in which:

FIG. 1 is a perspective view of a flotation machine constructed in accordance with this invention, with a portion of the exterior of the tank being broken away to show the impeller and stabilizer within the tank;

HO. 2 is a perspective view of the skeleton of the impeller of FIG. 1, i.e. prior to molding thereon a corrosion and abrasion resistant covering;

FIG. 3 is a horizontal section, taken along line 3--3 of FIG. 4 but with certain parts of the impeller and a stabilizer having a modified support broken away and shown in section, for clarity of illustration; and

FIG. 4 is a central vertical section taken along line 4-4 of FIG. 3.

The flotation machine of FIG. 1 includes a tank T which may be essentially conventional in construction,

being generally square or rectangular in lateral configu- 2 ration, and having a froth overflow lip 10 at one end and a bottom 11. The froth overflow lip 10 may be provided at one or at both opposite sides, while a conventional feed inlet and weir structure for the outflow of tailings or material to be discarded may be on the side adjacent the overflow or opposite thereto. The tank may also be'provided with a pulp level control weir which essentially determines the depth of the froth. These elements are all conventional and are therefore not shown, except for the froth overflow lip 10.

Installed normally centrally within the tank T and suspended by a tubular shaft 12, through which air may be supplied to the underside thereof, is an impeller l, which will be described in detail later. The shaft 12 is connected by a coupling 13 with a hollow shaft 14 which extends upwardly within a bearing housing 15, within which air is supplied through an air pipe 16 to the interior of the hollow shaft. Shaft 14, the upper end of which may be provided with a suitable plug, extends above the bearing housing 15 and is connected, through a suitable reduction transmission, with a conventional drive motor (not shown). I

The skeleton of the impeller I, prior to the molding of a suitable corrosion and abrasion resistantelastomer thereto,.is shown in FIG. 2. Thus, the impellerl includes a lower plate 20 which is circular and provided with a circular hole 21 at the center, surrounded by bolt holes 22, for attachment of the lower end of shaft 12 thereto. The impeller also includes an upper plate 25 having a central opening 26, larger in diameter than hole 21 in the lower plate, and sloping outwardly from the central opening 26 to its outer periphery. The angle of the outward slope of upper-plate 25 may be altered considerably, although an angle of approximately 13 to the horizontal may be found to be suitable in many instances. A series of pump vane plates 27 are attached, as by welding, in perpendicular relation to and between the lower plate 20 and upper plate 25, with a rod or post 28 extending between the plates 20 and 25 at the-outer edges of the vane plates 27. Both the vane ,plates 27 and the rods 28 are attached in a suitable manner, as by welding, to the upper and lower plates and to eachother. Depending from the lower plate 20 is a circumferentially spaced series of finger plates 29 attached at their outer edges to depending rods or posts 30 and desirably welded to the underside of plate 20. The number of vanes, determined by the number of vane plates 27, may be varied considerably, although a series of radially extending, equally spaced vane plates 22% apart will be found suitable in many instances. Also, the number of finger plates 29 may be varied, although twice the number of finger plates as vane plates may be found suitable in many instances. In the event that the number of vane plates and finger plates shown are utilized, alternate finger plate rods 30 may be integral with the vane rods 28, merely extending through a hole drilled in the lower plate 20 at an appropriate position. After the skeleton of the impeller I has been assembled, asin FIG. 2, the entire impeller is provided with a covering of an elastomer having suitable corrosion and abrasion resistant qualities. The thickness of the elastomer coating may be varied considerably, in accordance with the useage, and may also be varied at different portions of the impeller, depending upon the wear expected at such portions. The elastomer coating may be rubber or plastic, such as a suitable polyvinyl chloride.-

The elastomer coating 31 on the impeller is molded on the impeller skeleton so that a series of vanes 35, as in FIG. 3, and a series of depending fingers. 36 are formed, with both the vanes and fingers extending radially and each having a greater lateral thickness adjacent its outer edge than adjacent its inner edge. Also, the vanes each have a convex, rounded and conveniently arcuate inner edge 37 and outer edge 38, while the fingers 36 also have a convex, rounded and preferably arcuate inner edge 39 and outer edge 40. The radial length of the fingers 36 is preferably less than the radial length of the pumpingvanes 35, such as about 1/4 to H2 the length thereof. The impeller I, as in FIGS. 3 and 4, is mounted on the lower end of shaft 12 by .a ring 41 which is secured, as by welding, to the lower end of the shaft, and a series of bolts v42 which extend through bolt holes 22 of FIG. 2. Both the bolts 42 and the nuts 43 therefor are provided with an elastomer coating 31 which, in the case of rubber, is applied to the assembly, after attachment to the shaft, and then vulcanized. If desired, the exterior of shaft 12 may also be coated with an elastomer. Since air only passes down the inside of the shaft, it is unnecessary to provide an elastomer coating there.

The stabilizer S includes a plurality of vanes 45, as in FIG. 1, which extend radially from the impeller, the vanes being rectangular but of differing lengths, since the vanes extend outwardly to a supporting bar 46 which has a rectangular or square configuration corresponding to the inside of the tank T. The inner edges of the vanes 45 are spaced a short distance from the periphery of the impeller I, preferably with a clearance, such as 1 inch, greater than that necessary for normal clearance, to accommodate lateral whipping of the suspended impeller as it comes up to speed. The support bars 46 are, in turn, supported at each of the four corners by an angular bracket 47 which is mounted on the bottom of the tank and holds the lower edges of the stabilizer vanes 45 in spaced relation to the tank, with the impeller I being suspended at a height such that the clearance between the lower ends of the depending fingers 36 and the bottom of the tank is approximately the same as the clearance between the lower edges of the stabilizer vanes and the bottom of the tank. If desired, the stabilizer vanes 45 may be of equal length, with the supporting bars 46 forming a circle.

Each vane 45 of the stabilizer S may be merely a rectangular plate 48, as in FIG. 4, welded at the outside to the supporting bar 46 of FIG. 1, or may be bevelled at the lower outside corner, so that each supporting bar 46' of FIG. 4 will be disposed at about 45 to the plane of the tank bottom. Instead of the brackets 47 of FIG. 1, alternative brackets 49 may be utilized, having a flange 50 at the upper end extending at the same 45 angle as the bars 46', and a perpendicular flange 51 at the bottom attached to the bottom 11 of the tank, or merely resting on the bottom of the tank, with suitable provision for lateral restraint, such as an angle attached to the bottom of the tank and against the outside of which the brackets 47 or 49 abut.

The support bars 46 and 46', as well as the plates 48 and the brackets 47 or 49, are provided with an elastomer covering 31, conveniently molded thereto, and if rubber, then vulcanized. In addition, the bottom 11 of the tank is provided with a wear pad 55 having a molded elastomer covering 31 thereon which extends between the walls of the tank, except for cutouts 56 at the corners, to accommodate the brackets 47 or 49.

As in FIG. 3, the elastomer covering for the stabilizer or diffuser vanes'45 is preferably molded so that the lateral thickness of the vanes will be greater adjacent the inner edge than adjacent the outer edge, i.e., directly opposite to the configuration of the pumping vanes 35 and the fingers 36.'Also, the inner edge 57 of each diffuser vane 45 is convex and rounded, preferably arcuate, while the outer edge 58 may have any configuration, such as transverse to the plane of the plate 48.

As indicated previously, the lower edges of the fingers 36 are preferably spaced the same distance from the bottom of the tank as the lower edges of the vanes 48. Similarly, the upper edge of the impeller I may be approximately the same height, or spaced a short distance above the upper edges of the diffuser vanes 45.

Also, while the pump vanes 35 and fingers 36 extend radially of the impeller, each may be curved, to increase the pumping action in one direction, although a radial position of the vanes and fingers may be preferred, since after the elastomer on one side of the vanes and fingers has worn sufficiently to require replacement, the direction of rotation of the impeller may be reversed and the other side used until worn.

Considering now FIGS. 1 and 4, it will be evident that, with the impeller rotating in'either direction at an appropriate speed, the pulp in the bottom of the tank will be agitated and thrown outwardly into the spaces between the vanes of the stabilizer S by the depending fingers 36. At the same time, the pumping vanes 35 will suck pulp downwardly around the shaft 12, and pump this pulp outwardly into the spaces between the diffuser vanes. The inclination of the top of the impeller I tends to cause the velocity inside the impeller and velocity of discharge to be similar. The impeller I'tends to produce a swirling motion to the pulp, which is broken up by the vanes of the stabilizer S. In addition, the recirculation discharge from the pump portion of the impeller will cause a high degree of agitation of the pulp, both within and above the diffuser or stabilizer, through an intermixing of the pulp discharged from the pump portion of the impeller with the pulp discharged from the lower portion of the impeller. In any event, it has been observed that the combination of the upper pump and the lower agitator and pumper of the impeller produces a more violent agitation of the pulp within and above the diffuser S than an agitator or a closed impeller alone.

.Thus, it has been observed that the violent agitation,

particularly directly above the stabilizer S, causes the air bubbles to be subdivided and as a result, a greater number of air bubbles produced to act on the particles to be floated off.

It has also been observed that there are essentially three zones in the machine constructed in accordance with this invention, i.e., a first or lower zone which extends from the bottom of the tank upwardly to approximately 2 'or 4 inches above the top of the stabilizer S, in which zone there is violent agitation and some feed to the pump of the impeller I. The second or intermediate zone is above the first zone and extends up to approximately 2/3 to 3/4 of the height of the pulp level determined by the position of the froth overflow lip 10 of FIG. 1 and the weir bars for waste, in which the pulp becomes progressively quiescent, with the remainder of the feed around shaft 12 downwardly toward the intake opening of the pump of the impeller I. The third or upper zone, approximately the upper H3 or l-/4 of the pulp body, is relatively quiescent, except for air bubbles carrying recoverable material upwardly in this zone. In this zone, the mechanical lifting of particles,

extending through substantially theentire range of 5 sizes, occurs without material assistance from the pumping effect of the .impeller.

For test purposes, an impeller constructed in accordance with this invention was substituted for the impeller of each of ten Galigher No. 48 flotation machines, in a mill separating fluorite from gangue which included calcite, with the deslimed feed size of these rougher cells being as follows:

+28 mesh 8% +60 mesh 40% +350 mesh Balance Since the coarser sand, such as +60 mesh and particularly +28 mesh, has a tendency to settle more readily than the finer sand, the feed to these cells was considered to be an adequate test of their capabilities.

Thus, it was found that the peripheral speed of the impeller could be reduced from 1,170 feet per minute to'780 feet per minute; that the feed rate could be increased from 2,100 metric tons to 3,150 metric tons per day; that the precentage of mineral recovery was increased by 11.9 percent; and that the power consumption'per cell was lowered from 3.825 horsepower to 2.95 horsepower, a saving of 22.8 percent. It was also noted that the pulp body had little tendency to oscillate upwardly and downwardly and that there was no tendency for sand, particularly the coarser sand, to collect at the bottom of the tank, particularly in the corners. Each of the test machines had a stabilizer with outwardly extending vanes which were uniform in thickness, rather than tapering, as in the preferred form of this invention. However, other tests have indicated the desirability of the tapered stabilizer vanes.

When any flotation cell is stopped, there is a tendency for sand to settle out and collect in the bottom of the tank which, for a shutdown of between 5 and 10 minutes, but without further feed, required manual assistance in the case of previous machines for starting up after such a shutdown. However, the machines of the present invention started up much more readily and without manual assistance.

Although a preferred embodiment of this invention has been illustrated and described and certain variations thereof shown or indicated, it will be understood that other embodiments may exist and that other variations may be made, all without departing from the spirit and scope of this invention.

What is claimed is:

l. A rotatable impeller for a flotation machine, comprising:

a circular lower plate;

a circular upper plate concentric with and spaced from said lower plate, said upper plate having a circular central opening therein;

a series of vanes extending generally radially and disposed between said upper and lower plates, said vanes being constructed and arranged to pump pulp and the like from said central opening of said upper plate and discharge the same from the periphery of the space between said plates; and

lower plate and depending therefrom, said depending fingers being equally spaced about the periphcry of the underside of said lower plate, having a radial length less than the radial length of said vanes and having a lateral thickness adjacent the outer edge greater than adjacent the inner edge thereof.

2. An impeller as defined in claim 1, wherein the vertical distance between said upper and lower plates is greater adjacent said central opening than adjacent the periphery of said plates.

3. .An impeller as defined in claim 1, wherein the lateral thickness of said vanes is greater adjacent the periphery of said plates than adjacent said central openmg.

4. An impeller as defined in claim 3, wherein said vanes are equally spaced and each vane has substantially the same lateral thickness at different points along the radial length thereof as the other vanes.

5. An impeller as defined in claim 4, wherein the centerline of each said vane lies in approximately a radius of said plates..

6. An impeller as defined in claim I, wherein both the inner upright edge and the outer upright edge of said fingers is rounded and convex.

7. An impeller as defined in claim 1, wherein:

the vertical distance between said upper and lower plates is greater adjacent said central opening than adjacent the periphery of said plates;

'said vanes are equally spaced, and each vane has substantially the same lateral thickness at different points along the radial length thereof as theother vanes; and

both the inner upright edge and the outer upright edge of said fingers is rounded and convex.

8. In a flotation machine having a tank, the combination with an impeller as defined in claim 7, of:

a series of generally radial, upright vanes disposed outwardly from and surrounding said impeller adjacent the bottom of said tank;

means for supporting said outward vanes to hold said vanes with the lower edges thereof spaced from the bottom of said tank;

means for rotating said impeller about a vertical axis supporting said impeller with the lower ends of said depending fingers spaced from the bottom of said tank and including a hollow shaft for supplying an aeration fluid to the underside of said impeller;

said outward vanes having a lateral thickness adjacent the inner edge greater than the lateral thickness adjacent the outer edge thereof and the inner edges of said vanes being rounded and convex; and

the upper inner edges of said outward vanes being disposed above the outer upper periphery of said impeller and the lower ends of said depending fingers and the lower edges of said outward vanes are disposed at approximately the same height above said tank bottom.

'9. A rotatable impeller for a flotation machine, comprising:

a circular lower plate; a circular upper plate concentric with and spaced from said lower plate, said upper plate having a circular central opening therein; and

a series of vanes extending generally radially. and disposed between said upper and lower plates, said vanes having a greater lateral thickness adjacent the periphery of said plates than adjacent said opening and both the inner upright edge and the a series of vanes extending generally radially and disposed between said plates;

a series of fingers extending vertically from one of said plates and spaced around the periphery thereof;

of a series of generally radial, upright vanes disposed outwardly from and surrounding said impeller adjacent the bottom of said tank;

means for supporting said outward vanes with the lower edges thereof spaced from the bottom of said tank; and a hollow shaft forrotating said impeller about a vertical axis with the lower edge of said impeller spaced from the bottom of said tank, said hollow shaft supplying an aeration fluid to the underside of said impeller.

11. In a flotation machine as defined in claim 10,

wherein:

said outward vanes have a lateral thickness adjacent the inner edge greater than the lateral thickness adjacent the outer edge thereof.

12. In a flotation machine as defined in claim 11,

wherein:

the inner edges of said outward vanes are rounded and convex.

13. In a flotation machine as defined in claim l0,

p 8 wherein:

said outward vanes are equally spaced about the periphery of said impeller and the outer edges of said outward vanes correspond generally to a rectangle.

14. In aflotationmachineas defined in claim 10, wherein:

the upper inner edges of said outward vanes are disposed above the outer upper periphery of said impeller. V 15. In a flotation machine as defined in claim 14, wherein:

the lower edges of said depending fingers and the lower edges of said outward vanes are disposed at approximately the same height above said tank bottom. 16. In a flotation machine having a tank:

an impeller disposed adjacent the bottom of said tank, having upper pumping means for receiving pulp and the like centrally and from above and discharging the same outwardly, and lower agitation and pumping means for agitating and moving outwardly pulp and the like from the underside of said impeller;

means for rotating said impeller and supporting said impeller spaced from the bottom of said tank;

means for supplying an aeration fluid to said lower agitating and pumping means;

means surrounding said impeller, for receiving a pulp mixture from both said upper pumping means and said lower agitating and moving means, for interrupting the circular flow of said pulp mixtures and for producing an intermixing of said pulp mixtures with said aeration fluid; and

means for supporting said means surrounding said impeller at a position above the bottom of said tank corresponding to the position of said impeller. =l 

1. A rotatable impeller for a flotation machine, comprising: a circular lower plate; a circular upper plate concentric with and spaced from said lower plate, said upper plate having a circular central opening therein; a series of vanes extending generally radially and disposed between said upper and lower plates, said vanes being constructed and arranged to pump pulp and the like from said central opening of said upper plate and discharge the same from the periphery of the space between said plates; and a series of fingers spaced around the periphery of said lower plate and depending thErefrom, said depending fingers being equally spaced about the periphery of the underside of said lower plate, having a radial length less than the radial length of said vanes and having a lateral thickness adjacent the outer edge greater than adjacent the inner edge thereof.
 2. An impeller as defined in claim 1, wherein the vertical distance between said upper and lower plates is greater adjacent said central opening than adjacent the periphery of said plates.
 3. An impeller as defined in claim 1, wherein the lateral thickness of said vanes is greater adjacent the periphery of said plates than adjacent said central opening.
 4. An impeller as defined in claim 3, wherein said vanes are equally spaced and each vane has substantially the same lateral thickness at different points along the radial length thereof as the other vanes.
 5. An impeller as defined in claim 4, wherein the centerline of each said vane lies in approximately a radius of said plates.
 6. An impeller as defined in claim 1, wherein both the inner upright edge and the outer upright edge of said fingers is rounded and convex.
 7. An impeller as defined in claim 1, wherein: the vertical distance between said upper and lower plates is greater adjacent said central opening than adjacent the periphery of said plates; said vanes are equally spaced, and each vane has substantially the same lateral thickness at different points along the radial length thereof as the other vanes; and both the inner upright edge and the outer upright edge of said fingers is rounded and convex.
 8. In a flotation machine having a tank, the combination with an impeller as defined in claim 7, of: a series of generally radial, upright vanes disposed outwardly from and surrounding said impeller adjacent the bottom of said tank; means for supporting said outward vanes to hold said vanes with the lower edges thereof spaced from the bottom of said tank; means for rotating said impeller about a vertical axis supporting said impeller with the lower ends of said depending fingers spaced from the bottom of said tank and including a hollow shaft for supplying an aeration fluid to the underside of said impeller; said outward vanes having a lateral thickness adjacent the inner edge greater than the lateral thickness adjacent the outer edge thereof and the inner edges of said vanes being rounded and convex; and the upper inner edges of said outward vanes being disposed above the outer upper periphery of said impeller and the lower ends of said depending fingers and the lower edges of said outward vanes are disposed at approximately the same height above said tank bottom.
 9. A rotatable impeller for a flotation machine, comprising: a circular lower plate; a circular upper plate concentric with and spaced from said lower plate, said upper plate having a circular central opening therein; and a series of vanes extending generally radially and disposed between said upper and lower plates, said vanes having a greater lateral thickness adjacent the periphery of said plates than adjacent said opening and both the inner upright edge and the outer upright edge of said vanes is rounded and convex.
 10. In a flotation machine having a tank, the combination with an impeller having: a pair of vertically spaced, concentric circular plates, each of said plates having a central circular opening, with one opening being smaller than the other; a series of vanes extending generally radially and disposed between said plates; a series of fingers extending vertically from one of said plates and spaced around the periphery thereof; of a series of generally radial, upright vanes disposed outwardly from and surrounding said impeller adjacent the bottom of said tank; means for supporting said outward vanes with the lower edges thereof spaced from the bottom of said tank; and a hollow shaft for rotating said impeller about a vertical axis with the lower edge of said impeller spaced froM the bottom of said tank, said hollow shaft supplying an aeration fluid to the underside of said impeller.
 11. In a flotation machine as defined in claim 10, wherein: said outward vanes have a lateral thickness adjacent the inner edge greater than the lateral thickness adjacent the outer edge thereof.
 12. In a flotation machine as defined in claim 11, wherein: the inner edges of said outward vanes are rounded and convex.
 13. In a flotation machine as defined in claim 10, wherein: said outward vanes are equally spaced about the periphery of said impeller and the outer edges of said outward vanes correspond generally to a rectangle.
 14. In a flotation machine as defined in claim 10, wherein: the upper inner edges of said outward vanes are disposed above the outer upper periphery of said impeller.
 15. In a flotation machine as defined in claim 14, wherein: the lower edges of said depending fingers and the lower edges of said outward vanes are disposed at approximately the same height above said tank bottom.
 16. In a flotation machine having a tank: an impeller disposed adjacent the bottom of said tank, having upper pumping means for receiving pulp and the like centrally and from above and discharging the same outwardly, and lower agitation and pumping means for agitating and moving outwardly pulp and the like from the underside of said impeller; means for rotating said impeller and supporting said impeller spaced from the bottom of said tank; means for supplying an aeration fluid to said lower agitating and pumping means; means surrounding said impeller, for receiving a pulp mixture from both said upper pumping means and said lower agitating and moving means, for interrupting the circular flow of said pulp mixtures and for producing an intermixing of said pulp mixtures with said aeration fluid; and means for supporting said means surrounding said impeller at a position above the bottom of said tank corresponding to the position of said impeller. 